Impact of mesoscale meteorological processes on anomalous radar propagation conditions over the northern Adriatic area

Abstract

The impact of mesoscale structures on the occurrence of anomalous propagation (AP) conditions for radio waves, including ducts, superrefractive, and subrefractive conditions, was studied. The chosen meteorological situations are the bora wind and the sporadic sea/land breeze (SB/LB) during three selected cases over a large portion of the northern Adriatic. For this purpose, we used available radio soundings and numerical mesoscale model simulations (of real cases and their sensitivity tests) at a horizontal resolution of 1.5 km and 81 vertical levels. The model simulated the occurrences of AP conditions satisfactorily, although their intensities and frequency were underestimated at times. Certain difficulties appeared in reproducing the vertical profile of the modified refractive index, which is mainly dependent on the accuracy of the modeled humidity. The spatial distributions of summer AP conditions reveal that the surface layer above the sea (roughly between 30 and 100 m asl) is often covered by superrefractive conditions and ducts. The SB is highly associated with the formations of AP conditions: (i) in the first 100 m asl, where trapping and superrefractive conditions form because of the advection of cold and moist air, and (ii) inside the transition layer between the SB body and the elevated return flow in the form of subrefractive conditions. When deep convection occurs, all three types of AP conditions are caused by the downdraft beneath the cumulonimbus cloud base in its mature phase that creates smaller but marked pools of cold and dry air. The bora wind usually creates a pattern of AP conditions associated with the hydraulic jump and influences distribution of AP conditions over the sea surface.

Wind Over the Adriatic Region in CORDEX Climate Change Scenarios

“…Bora can also gradually extend from northern Adriatic along the eastern Adriatic coast toward the southern Adriatic, which often corresponds to anticyclonic movement. Case studies (e.g., Gohm et al, 2008;Prtenjak et al, 2015) have revealed that anticyclonic Bora cases are usually deeper, with weaker winds than those of the cyclonic Bora cases. Large-scale atmospheric conditions over Europe that sustain different Bora and Sirocco types over the eastern Adriatic Sea are investigated in Pandžić and Likso (2005).…”

“…Large-scale atmospheric conditions over Europe that sustain different Bora and Sirocco types over the eastern Adriatic Sea are investigated in Pandžić and Likso (2005). The climatology of the present-day Bora wind, which is obtained from observations at meteorological stations (e.g., Poje, 1992), from satellites (Zecchetto & Cappa, 2001), and from simulations (Horvath et al, 2011;Prtenjak et al, 2015;Stiperski et al, 2012), reveals that Bora wind is the strongest, most frequent, and persistent over the northeastern Adriatic (i.e., the region around Senj). The main characteristic of the Bora wind is the spatial variation in wind speed (Grisogono & Belušić, 2009;Prtenjak et al, 2015) due to the formation of alternating Bora jets and wakes along the coast.…”

Process‐based evaluation of the VALUE perfect predictor experiment of statistical downscaling methods

“…The typical bora wind is a gusty downslope flow perpendicular to a mountain ridge along the Adriatic Coast, almost always from the NE quadrant. Certain observed differences in the bora characteristics arise from the synoptic pressure pattern over Europe (Pandži c and Lisko, 2005;Horvath et al, 2009;Prtenjak et al, 2015). Cyclonic ("dark") bora is typically a result of a Mediterranean cyclone (mostly formed over the Adriatic or Gulf of Genoa) and is associated with strong winds and precipitation.…”

“…The characteristics of bora flow, and consequently the temperature and humidity fields, are highly influenced by the geographical location and complex coastal topography. The main characteristic of the bora wind is its spatial variation in wind speed (Grisogono and Beluši c, 2009;Prtenjak et al, 2015) due to the formation of alternating bora jets and wakes along the coast. The bora jets are linked to the mountain gaps (Grubiši c, 2004;Kuzmi c et al, 2013) and hence, affect locally the bora wind duration and strength in meteorological and climatological analyses (Poje, 1992;Beluši c et al, 2017).…”

Inversion for Inhomogeneous Surface Duct without a Base Layer Based on Ocean-Scattered Low-Elevation BDS Signals

“…The transmitting environment is universally preset to be the normal atmosphere for radio systems operating in the lower atmosphere. However, the meteorological element fields in the atmospheric boundary layer are variable, and the resultant abnormal propagation conditions will seriously affect the regular operation and performance evaluation of radio devices [1][2][3]. Notably, the trapping structures formed in the states of temperature and humidity inversion, i.e., tropospheric ducts, can make the radio waves propagate towards the ground, resulting in the occurrence of over-the-horizon propagation [4,5].…”